Enhancement of solute spreading in soils due to particle-facilitated transport and preferential flow

A process-based modelling approach of organic contaminant spreading is presented, which allows to quantify the increase of groundwater pollution risk due to preferential flow and particle-facilitated transport in the vadose zone. Both effects are illustrated by means of a parameter study based on realistic input data. When coupled with biodegradation, preferential flow and particle-facilitated transport lead to an increase in the long-term concentration to be expected at the groundwater table as both processes reduce the bioavailability of the contaminant due to either shorter residence times (preferential flow) or lower accessibility (particle-facilitated transport). Model predictions account for the amount and the velocity of preferential flow as well as the potentially kinetic interaction between organic contaminant and mobile particles.